Method and system of motor control and switch operated thereby



March 7, 1944.

F. H. ROBY METHOD AND SYSTEM OF MOTOR CONTROL AND SWITCH OPERATEDTHEREBY Original Filed April 21, 1941 3 Sheets-Sheet 1Illlllfljlllllllllllllll lllllll JSBEHZXQQJZLELQ E BY INVENTOR ATTORNEYMarch 7, 1944. F, H. ROBY 2,343,801

METHOD AND SYSTEM OF MOTOR CONTROL AND SWI-TCH OPERATED THEREBY OriginalFiled April 21, 1941 3 Sheets-Sheet 2 INVENTOR $472 PaZy ATTORNEY March7, 1944. F. H. ROBY 2,343,801

METHOD AND SYSTEM OF MOTOR CONTROL AND SWITCH OPERATED THEREBY OriginalFiled April 21, 1941 3 Sheets-Sheet 5 w w 'E- I r 7 INVENTOR PatentedMar. 7, 1944 METHOD AND SYSTEM OF MOTOR CON- TROL AND SWITCH OPERATEDTHEBEBY Frank 11. Roby, Milwaukee, Wla, m to Square D Company, Detroit,Mich, a corporation of Michigan Original application, April 21, 1941,Serial No.

389,548. Divided and this application September 10, 1942, Serial No.457,863

8 Claims.

This invention relates to a method and system for braking alternatingcurrent motors and to an electric motor driven timing switch employingsuch method and system to determine the stopping point of the timingswitch, and constitutes a division of my application Serial No. 389,548,filed April 21, 1941, for Method and system for electric welding.

An object of this invention is to provide a new and improved method orsystem for plugging or braking alternating current motors to a stop.

Another object of the invention is to provide a method and system ofbraking alternating current motors :by a control condenser dischargethrough the motor with the condenser discharge determined by apredetermined point of current interruption.

Another object of the invention is to provide a motor driven timingswitch including a plurality of sequentially operated electricalcontacts in which a condenser discharge is utilized to stop the drivingmotor at a predetermined position so that the operating contacts will beoperated in proper sequence when the motor is again started.

Other objects and features of the invention will be readily apparent tothose skilled in the art from the specification and appended drawingsillustrating certain preferred embodiments in which:

Figure 1 is a front elevational view of a control panel for an electricwelder system embodying the features of the present invention.

Figure 2 is a horizontal sectional view taken on the line II-II ofFigure 1.

Figure 3 is a sectional view on the line III-III of Figure 1.

Figure 4 is a schematic representation of a welding machine in which thewelder system which embodies the timing switch and method and system ofmotor plugging or braking may be used.

Figure 5 is a view showing the internal wiring diagram of the panel ofFigure 1.

Figure 6 is a diagrammatic view of the wiring connections and equipmentexterior to the panel of Figure 5.

Figure 7 is a simplified schematic wiring diagram.

Figure 8 is a circle diagram showing points of type, synchronous motorindicated generally at I. A condenser 4 is provided for one of the motorwindings and also provided on the board are a reactor 5, a controltransformer I, a pair of electromagnetically operated electric switchesI and 8. and a plugging condenser 8.

The timing switch 2 shown more particularly in Figures 1, 2 and 3,comprises a pair of stationary supporting members II and i2 havingcentral hubs containing hearings in which is rotatably disposed theoperating shaft it upon which are mounted the contact operating cams l4,it, i8, l1, It, It and 2|. On opposite sides of the stationary supportsii and I2 are rotatably mounted the contact supporting plates 22, 23, 24and 25, these plates being normally held stationary by the springclip;indicated at 28, but being rotatable by means of handle elements 21rigidly mounted on the plates so that their relation with respect to theoperating shaft I3 and the cams may be adjusted. Upon each of the plates22, 23, 24 and 25 are pivotally mounted contact arms 28 biased bysprings 29 toward contacts engaged position. Contact arms 28 carrymovable contact 2! adapted to cooperate with stationary contacts 22 onthe plates. The contact arms 22 carry rollers .33 which engage theirrespective cams to effect rotation of the contact arms to eiIectengagement and disengagement of the cooperating contacts 3| and 32. Theshaft I3 is driven through gearing 24 and through a reduction gearmechanism incorporated in the motor 3 and the speed of rotation of theshaft i3, and hence the speed of the welding cycle may be varied bychanging the gearing 14, a suitable group of interchangeable gearelements being provided on the panel at 35. The movable contact on plate24 has been indi-- cated at 3!. A similar movable contact on Plate 22 isindicated at 36 and the movable contacts on plates 23 and 25 areindicated at 21 and 38 respectively. At the left hand end of the shaftl3 and cooperating with the insulating cam elements I4, l5 and it arethree relatively light sets of contacts 39, 4i and 42. The contact sets39 and 42 are formed to be closed on the high part of the cam andcontact set 4| is formed to be open on the high part of the cam. Thepoints of operation of thecams I4, l5 and It may be determined byvarying their position upon the shaft l3. Ordinarily, the cams l5 and itwill have a relatively fixed setting and the cam l4 will be readilyadjustable since its point of fixed operation determines the position ofthe parts at rest, as will be explained hereinafter.

The electromagnetic switch or relay 1 on the the position of the upperelectrode.

panel includes an operating coil II and four sets of cooperatingcontacts, a normally closed set of contacts ll and three sets ofnormally open contacts ll, 4! and 41 shown in the Figures 5 and "l. Theelectromagnetic switch or relay I comprises an operating coil is andfour sets of cooperating contacts, two of the sets, l! and II, beingnormally closed and two sets, I! and I8, being normally open.

Figure 4 shows a schematic diagram of a'welding tool or machine. Thiscomprises a frame 84 having an operating cylinder ll within which ispiston ll carrying a movable electrode II. A stationary electrode 88 issupported in the items! through an insulating bushing II, power beingled to the electrodes through conductors ii from the secondary of thewelder transformer, not here shown. The movements of the piston I arecontrolled through a solenoid valve which comprises an operating winding82 and a slide 68. A source of fluid pressurel m fltois dpit'glvindled.

ed the solenoi ve e ne eontroll y n e p s tionshowninPigure4,thecoil l2hasjustbeen deeneiaized so that the source of fluid pressure has nowbeen connected to the underside oi the piston whereupon the movableelectrode will move upwardly to release the work as at the comon of awelding cycle.

i: the external wiring diagram of Figure 6, in addition to the partspreviously described, there are shown a push button control switch 6!, awelding transformer Cl. and a contactor in the primary of the weldingtransformer circuit which includes an operating coil 81 and coopcratingcontacts I. Associated with this contactor is a synchronizing featuresupplied by the auxiliary synchronizing coil 0! energized by thesecondary of a transformer 'II in whose primary circuit is an adjustableresistor 12, adjustment of the resistor 12 determining the point on thesupply wave at which the contacts separate, this contactorsynchronization being more fully described and claimed in the copendingapplication of Ernest G. Anger, Serial No. 204,052, filed April 25,1938, for Electric switch.

Figure 8 is a circle diagram representing the points of actuation of thecontacts, of the motor driven timing switch. It is understood that allof the contacts are adjustable in that either their mounting platesand/or their operating cams are adjustable with respect to the shaft l3.In the ordinary operation only the contacts 31, II and I8 and ll willrequire adjustment, the contacts ll, 82 and ll having a relativeLv fixedsetting. The system provides a constant point of rest for the operatingmotor and timing switch. which constantstop point has been indicated atH on the circle diagram of contact operation,

The other points indicated on this diagram are as follows: point A wherecontact 31 opens; point B at which contact 42 opens; point C at whichcontact "closes; point D at which contact ll closes: point E at whichcontact 3! opens; point 1' at which contact 3| closes and point G atwhich contact 38 opens. The points at which the alternative contactoperations occur, 1. e.. the opening points for the contacts hereinreferred to as closing and the closing point for the contacts referredto as opening, do not affect the operation ofthe system.

To initiate a welding cycle after the work has been placed between theelectrodes. the operator presses the push button starting switch 8!.This may be only momentarily closed for a single weld, or the pushbutton may be maintained closed to effect a plurality of welds in aseries. Upon the closing of the push button switch II. the operatingcoil 48 of the relay or switch I is immediately energized, closing itscontacts ll, ll, and 41 and opening contact 44. The closing of contact41 forms a holding circuit for the operating coil 33 through thenormally closed contact 40 of relay or switch 8. The closing of contactll immediately energizes the operating coil 52 of the solenoid valvethrough the normally closed contact ii of the relay 8. When the coil 82is energized, the solenoid valve operates to apply pressure to the upperside of the piston Bl diagrammatically shown in Figure 4, whereupon themovable electrode I1 descends to apply pressure to the work. The closingof contact ll energizes the synchronous motor 3 which then acceleratesto its full operating speed. The opening of contact 44 disconnect; thecircuit through the plugging condenser 8 to disconnect it from aroundthe motor 3 during the normal operation of the system.

The operating shaft ll of the motor driven timing switch I rotates fromthe position of point H, which was taken as the rest point of the shaft,to the first point reached at A where contact 31 opens. This, however,has no eiiect in single welds and in the first of a series of welds,since the holding circuits about contact I! is still provided by thenormally closed contact Bl of relay 8. It is this normally closedcontact which effects the additional "delay" time which is added to thenormal "squeeze" time in single welds and in the first of a series ofwelds, as will be explained hereinafter. The cam shaft It continues torotate until point B is reached, at which point contact 42 opens, againwithout effect since coil 43 is energized through the normally closedcontact 4! of relay I. The cam shaft continues to rotate to point C atwhich contact it closes but again without eii'ect since the solenoidvalve is already energized through the normally closed contact ll. Atthe next point D contact ll closes to effect energization of theoperating coil ll of the relay I through the now closed contact 48 ofrelay 1.

Relay 8 is energized to eii'ect opening of contacts 49 and 5| andclosing of contacts 52 and II. The closing of contact 53 forms a holdingcircuit for contacts 58 around the cam operated contact Al. The openingof contact 5! opens the holding circuit about contacts 36 and 31 to thesolenoid valve 62 and now places the control of the solenoid valve inthe parallel connected, cam operated contacts i6 and 31. The opening ofcontact 89 removes the holding circuit around the cam operated contact42 and places the control of the operating coil 43 in cam driven contactI! when the push button 65 is released. The closing of contact 52 setsup the circuit to the operating coil 81 for the contacts 68 in thecircuit to the primary of the welding transformer. As the cam sh'ai't I3continues to rotate, at point E the contact 39 is opened, but withouteffect, since it is short circuited by the now closed contact ll. Atpoint F in the rotation of the cam shaft, contact 3| closes and thisefl'ects energization of the energizing coil 81 to close the contact 88,and energizes the welding transformer to start the ilow of currentthrough the weld. The current continues to flow until point G isreached, at which point contact ll opens to deenergize the coil 81 andeffect opening of the contact 88. If a synchro-break contactor isemployed of the type disclosed in application Serial No. 204,052aforesaid, the opening point of the contact 68 will be furthercontrolled by the adjustment of the current in the auxiliarysynchronizing coil 89. This interruption of the current completes theweld period in the welding cycle. As the shaft l3 continues to rotate,the point A is again reached and now the opening of contact 31 effectsdeenergization of the operating coil 62 of the solenoid valve andremoves the pressure on the welding electrode to release the work.

If the push button has been maintained depressed, the shaft continues torotate without operation in the system until point C is reached whencontact 86 closes to again energize the operating coil 62 of thesolenoid valve and reestablishwelding pressure on the work. At points Fand G, the welding current is applied and interrupted, and at point Athe pressure is again released. This repetition of sequential pressureand current application and release is carried out to make successivewelds in a series of welds so long as the push button is remaineddepressed.

Whenever the push button is released, either at the end of a series orafter being momentarily closed for a single weld, the operationspreviously described take place and when the cam shaft reaches point Bafter the push button is released (and at least one weld completed) theopening of contact 12 effects deenergization of the operating coil 33 ofthe relay 1. The deenergization of this relay effects closing of contact44 and opening of contacts 45, 46 and 41. The opening of contact 46effects opening of the circuit to the solenoid valve 62 and deenergizesthe operating coil 48 of relay 8 whose deenergization effects opening ofcontacts 52 and 53 and closing of contacts 49 and I. The opening ofcontact 45 places the control of the motor circuit in the cam operatedcontacts 39. The closing of contact 44 again closes the circuit to theplugging condenser 9 which is now connected in parallel with the motorwinding. The opening of contact 52 opens the circuit to the weldercontactor and prevents closing thereof as the cam shaft continues torotate. After the operations just described, points C and D are passedin the rotation of the shaft without effecting operation of the elementsof the system, since the circuit thereto is open at contact 46. At thepoint E contact 39 is opened. This disconnects the motor from the lineand permits the condenser 9 to discharge through the motor winding. Thiscondenser discharge effects a very quick stopping of the motor and atthe same predetermined point, such as the point H indicated on thecircle diagram on Figure 8. The system is now at rest and is preparedfor the initiation of a new welding cycle.

The positioning of the motor at rest at a predetermined point in therotation of the cam shaft provides obvious advantages in the system,since it is unnecessary to have the motor rotate constantly andunnecessary to have an initiating relay which would be picked up at onepoint in the operation of the shaft. Furthermore, the positive positionof the motor at rest makes the total elapsed time between the closing ofthe push button and the making of the first weld become constant. Thispositive positioning further provides a definite delay time for singlewelds and the first weld in a series of welds. This plugging or brakingto a definite predetermined position is very emciently eflected by theuse of the plugging condenser 0 which feeds back or discharges throughthe motor winding to effect thequick stopping thereof. For mosteillcient operation, it is desired to have the condenser discharge tobrake the motor when the maximum energy is stored therein. It is furtherdesirable that this charge on the condenser for braking be maintainedconstant to avoid the possibility of variable braking which would occurif the motor and condenser were disconnected from the line at some pointother than current zero. Since the contact 39 is synchronously driven,the adjustment of its cam operator with respect to the shaft 31 may beset so as to insure opening of the contacts when the currenttherethrough has an instantaneous value of zero. To further effect thisinterruption of the motor circuit when the current is zero, the reactor5 is placed in series with the condenser so that should the contacts 39actually separate at a point other than current zero, throughmisadjustment thereof, the inductance in the circuit provided by thereactor 5 will cause arcing at the contact t ps to pass current untilthe arc is interrupted at the zero point of the current cycle.Accordingly, it is seen that the condenser and motor circuit will beinterrupted, either through the accurate positioning of the contactoperating cam or by the arcing at the contacts, when the current has aninstantaneous value of zero and a substantially constant and maximumcharge on the condenser will be used to effect constant braking of thedriving motor.

Again referring to the circle diagram of Figure 8, the portion of therotation of the cam shaft 13 represented by the are between point H andpoint C represents the delay time during which the pressure is buildingup on the work and which is utilized only for single welds and for thefirst in a series of welds. This additional time adds on to the squeeze"time normally provided for each weld in a continuous series of welds.The desire for this additional time for single and initial Welds isnecessitated by various factors such as additional friction in thewelding tool, a greater movement of parts, and other reasons whichrequire alonger time to build up adequate welding pressure after thesolenoid valve is energized after the system is at rest. This additionaldelay time is provided through the normally closed contact 5| of relay 8which permits energization of the operating coil 62 of the solenoidvalve immediately the contact 46 closes, which closing is affected whenthe push button is initially closed. However, contact 5| being openedwhen relay 8 is energized, places the control of the solenoid valve, solong as relay 8 remains energized, in the contacts 36 and 31 so thatafter the first weld in a continuous series of welds is completed, thesolenoid valve will therefore be energized only at the point C in thewelding cycle so that the delay time does not occur in other than insingle welds or in the first of a series of welds. In all welds, asqueeze time represented by the are between points C and F is provided.In the case of single welds and the first in a series of welds, thistime is simply added to the delay time represented by the are 1-1-6 sothat the total time between energization of the solenoid valve andapplication of current is represented by the long are H--F for singlewelds and the first in a series of welds. The "weld time in the weldingcycle is represented by the timing primary is energized to pass currentthrough the work. The "hold" time in the welding cycle is represented bythe arc H in which the pressure on the electrodes is maintained ai'tercurrent has ceased to flow. The "oil" time in the welding cycle where acontinuous series or welding cycles is being eilected is represented bythe arc A-C in which pressure is released.

lnthecirclediagramoil'lguresitisseenthat points B, C and D arerelatively constant and need not ordinarily be adiustedaiter the factoryadjustment oi the timing switch. However, points I, I. G and A are madereadily adjustable on the respect to point determines the squeeze timeand the relation 0! point G with respect to point 1'' determines the"weld" time, and the relation of point A with respect to point (3determines the stopping point of the motor and hence determines thedelay period which might vary with speciiic welding applications, as mayalso the minimum time required for the motor to accelerate thesynchronous speed. The adjustment of points i", G and H is effected bymovement of the handies 21 which rotate contacts 3|, 38 and 31 withrespect to the operating cam shaft and hence determine the points atwhich contact operation is eii'ected. The adjustment of point E may beeilected by changing the position or cam l4 on the cam shai't ll.

While certain preferred embodiments of the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

What is claimed is:

l. A motor driven timing switch comprising a plurality of sets ofcooperating contacts, motor driven means for effecting sequentialoperation of said contacts, control means for the motor, a condenser,and means connecting the condenser in parallel with the motor winding todischarge therethrough when the control means is operated to disconnectthe motor, means for eilecting the final opening of the circuit todisconnect the motor when the current therethrough has a predeterminedinstantaneous value so as to eflect a predetermined charge on thecondenser when the circuit is discontinued, said condenser dischargeeiiectively braking the motor and driven means to a stop in apredetermined position so that the contacts will be operated in propersequence when the motor is again started.

2. A motor driven timing switch comprising a plurality of sets ofcooperating contacts, motor driven means for eii'ecting sequentialoperation of said contacts, control means for the motor, a condenser,and means connecting the condenser in parallel with the motor winding todischarge therethrough when the control means is operated to disconnectthe motor, synchronously driven means for eiiecting operation of saidcontrol means to disconnect the motor when the current therethrough hasan instantaneous value of substantially zero to secure a maximum chargeon the condenser when the circuit is discontinued, the discharge oi thecondenser through the motor windings eflectlvely braking the motor anddriven means to a stop in a predetermined position so that the contactswill be operated in proper sequence when the motor is again started.

3. A motor driven timing switch comprising a switch. since the relationof point 1'' with.

control means to disconnect the 9,848,801 are F-G during which thewelding transformer plurality oi cooperating contacts, synchronous motordriven means ior eirecting the sequential operation 0! said contacts atpredetermined points upon the supply wave to the motor, lone 0! saidsets 0! contacts controlling the disconnection of the motor circuit andbeing set to disconnect said circuit when the current therethrough hasan instantaneous value oi substantially zero, a condenser, and meansconnecting said condenser in parallel with the motor winding so as todischarge therethrough when the motor circuit is interrupted, wherebythe motor and driven means will be eflectively braked to a predeterminedstop position so that the contacts will be operated in proper sequencewhen the motor is again started.

4. A motor driven timing switch comprising a plurality or sets ofcooperating contacts, motor driven means for effecting sequentialoperation of said contacts, control means for the motor, a condenser,and means connecting the condenser in parallel with the motor winding todischarge therethrough when the control means is operated to di connectthe motor, means providing an inductive component in the current throughsaid motor control means whereby opening or the motor will beaccompanied by arcing to maintain the -iiow oi current until it has aninstantaneous value of substantially zero to store the maximum energy inthe condenser, the discharge 0! the condenser through the motor windingsei'lectively braking the motor and driven means to a stop in apredetermined position so that the contacts will be operated in propersequence when the motor is again started.

5. The method of braking an alternating cur rent motor which comprisesconnecting a condenser in parallel with the motor winding to be chargedfrom the supply circuit to the motor, and providing for an inductivecomponent in the current through the control contacts for the motor toestablish arcing at the contact tips and insure final interruption ofthe circuit substantially at the zero point of the current cycle tosecure a maximum discharge of energy from the condenser through themotor winding and a maximum braking action on the motor.

6. A motor control circuit comprising an alternating current source, analternating current motor having its winding connected to said source,and a condenser connected in parallel with said motor winding anddischarging therethrough when the connection to the source is broken,and means for effecting interrupting oi the circuit to said source whenthe current has a predetermined instantaneous value to secure apredetermined discharge of energy from the condenser through the motorwinding to brake the motor to a stop.

"1. A motor control circuit comprising an alterhating current source, analternating current motor having its winding connected to said source, acondenser connected in parallel with said motor winding, synchronouslyoperated contacts for disconnecting said motor from the source, saidcontacts being set to interrupt said connection when the currenttherethrough has an instantaneous value of substantially zero, wherebythe maximum charge will be stored in said condenser at the instant thecircuit is broken, the stored energy thereafter discharging through themotor winding to brake the motor to a stop.

8. A motor control circuit comprising an alternating current source, analternating current motor having its winding connected to said source, acondenser connected in parallel with said motor winding, control meansfor the connection and disconnection of said motor .to the source, andmeans for providing an inductive 6 component in the current through saidcontrol means, whereby op ning the control mean will be accompanied byarcing to maintain the cir- FRANK H. ROBY,

